2. Section 1 Chordates

3. Animals with a backbone belong to a larger group of animals called chordates (KOR dayts). Three characteristics of all chordates are a notochord, a nerve cord, and pharyngeal pouches at some time during their development. What is a chordate? Chordate Animals 1 1

4. The notochord is a flexible rod that extends along the length of the developing organism. Pharyngeal pouches are slitlike openings between the body cavity and the outside of the body. What is a chordate? Chordate Animals 1 1

5. Scientists classify the 42,500 species of chordates into smaller groups. The animals within each group share similar characteristics, which may indicate that they have a common ancestor. Vertebrates Chordate Animals 1 1

6. Vertebrates have an internal system of bones called an endoskeleton. Endo- means “within.” Vertebrates Chordate Animals 1 1 The vertebrae, skull, and other bones of the endoskeleton support and protect internal organs.

7. Most vertebrate body temperatures change as the surrounding temperature changes. Body Temperature Chordate Animals 1 1 These animals are ectotherms (EK tuh thurmz), or cold-blooded animals.

8. Humans and many other vertebrates are endotherms (EN duh thrums), or warm- blooded animals. Their body temperature doesn’t change with the surrounding temperature. Body Temperature Chordate Animals 1 1

9. Body Temperature Chordate Animals 1 1 Changes of more than a degree or two usually indicate an infection or overexposure to extreme environmental temperatures.

10. Fish Chordate Animals 1 1 Fish have fleshy filaments called gills where carbon dioxide and oxygen are exchanged. Fish are ectotherms that can be found in almost all bodies of water, including warm desert pools and the subfreezing Arctic Ocean.

11. Most fish have pairs of fanlike fins. Fish Chordate Animals 1 1 The top and the bottom fins stabilize the fish. Those on the sides steer and move the fish. The tail fin propels the fish through the water.

12. Fish Chordate Animals 1 1 Most fish have scales. Scales are thin structures made of a bony material that overlap like shingles on a house to cover the skin.

13. Scientists classify fish into three groups—bony, jawless, and jawed cartilaginous (kar tuh LA juh nuhs). Types of Fish Chordate Animals 1 1 Bony fish have skeletons made of bone, while jawless fish and jawed cartilaginous fish have endoskeletons made of cartilage. Cartilage (KAR tuh lihj) is a tough, flexible tissue that is similar to bone but is not as hard or brittle.

14. About 95 percent of all fish have skeletons made of bone. Bony Fish Chordate Animals 1 1 The body structure of a typical bony fish is shown here.

15. Bony Fish Chordate Animals 1 1

16. An important adaptation in most bony fish is the swim bladder. This air sac helps control the depth at which the fish swims. Bony Fish Chordate Animals 1 1

17. Bony Fish Chordate Animals 1 1 As the swim bladder fills with gas, the fish rises in the water. Then the gas leaves the bladder, it deflates and the fish sinks lower in the water.

18. Most bony fish use external fertilization (fur tuh luh ZAY shun) to reproduce. Bony Fish Chordate Animals 1 1 Females release large numbers of eggs into the water. Then, a male swims over the eggs, releases the sperm into the water, and many eggs are fertilized.

19. Jawless fish have scaleless, long, tubelike bodies; an endoskeleton made of cartilage; and a round, muscular mouth without a jaw. Jawless and Jawed Cartilaginous Fish Chordate Animals 1 1 One type of jawless fish, the lamprey, attaches itself to a larger host fish using its strong mouth and toothlike structures.

20. Sharks, skates, and rays are jawed cartilaginous fish. Jawless and Jawed Cartilaginous Fish Chordate Animals 1 1 Jawed cartilaginous fish have rough, sandpaperlike scales and movable jaws. Many sharks have sharp teeth made from modified scales.

21. 1 1 Section Check Question 1 _______ is the internal system of bones in vertebrates. Answer The answer is endoskeleton. The endoskeleton supports and protects the internal organs.

22. 1 1 Section Check Question 2 Which is the largest group of vertebrates? A. cats B. dogs C. fish D. humans

23. 1 1 Section Check Answer The answer is C. Fish are ectotherms and live in water.

24. 1 1 Section Check Question 3 This illustration shows a typical body structure of what classification of fish? A. bony B. cartilaginous C. jawless D. scale less

25. 1 1 Section Check Answer The answer is A. About 95 percent of all fish have skeletons made up of bone.